The invention relates in particular to a method of providing flour doughs having improved rheological properties and to finished baked or dried products made from such doughs, which have improved textural, eating quality and dimensional characteristics.
In this connection, the “strength” or “weakness” of doughs is an important aspect of making farinaceous finished products from doughs, including baking. The “strength” or “weakness” of a dough is primarily determined by its content of protein and in particular the content and the quality of the gluten protein is an important factor in that respect. Flours with a low protein content is generally characterized as “weak”. Thus, the cohesive, extensible, rubbery mass which is formed by mixing water and weak flour will usually be highly extensible when subjected to stress, but it will not return to its original dimensions when the stress is removed.
Flours with a high protein consent are generally characterized as “strong” flours and the mass formed by mixing such a flour and water will be less extensible than the mass formed from a weak flour, and stress which is applied during mixing will be restored without breakdown to a greater extent than is the case with a dough mass formed from a weak flour. Strong flour is generally preferred in most baking contexts because of the superior rheological and handling properties of the dough and the superior form and texture qualities or the finished baked or dried products made from the strong flour dough.
Doughs made from strong flours are generally more stable. Stability of a dough is one of the most important characteristics of flour doughs. According to American Association of Cereal Chemists (AACC) Method 36-01A the term “stability” can be defined as “the range of dough time over which a positive response is obtained and that property of a rounded dough by which it resists flattening under its own weight over a course of time”. According to the same method, the term “response” is defined as “the reaction of dough to a known and specific stimulus, substance or set of conditions, usually determined by baking it in comparison with a control”
Within the bakery and milling industries it is known to use dough “conditioners” to strengthen the dough. Such dough conditioners are normally non-specific oxidizing agents such as eg iodates, peroxides, ascorbic acid, K-bromate or azodi-carbonamide and they are added to dough with the aims of improving the baking performance of flour to achieve a dough with improved stretchability and thus having a desirable strength and stability. The mechanism behind this effect of oxidizing agents is that the flour proteins, in particular gluten contains thiol groups which, when they become oxidized, form disulphide bonds whereby the protein forms a more stable matrix resulting in a better dough quality and improvements of the volume and crumb structure of the baked products.
In addition to the above usefulness of ascorbic acid/ascorbate as a cough conditioner due to its oxidizing capacity, these compounds may also act as substrate for an oxidoreductase, ascorbate oxidase which is disclosed in EP 0 582 116 A1. In the presence of its substrate, this enzyme converts ascorbic acid/ascorbate to dehydroascorbic acid and H2O2. This prior art does not suggest that ascorbic acid oxidase in the presence of ascorbic acid/ascorbate might have a dough conditioning effect, but assumingly this is the case.
However, the use of several of the currently available oxidizing agents is either objected to by consumers or is not permitted by regulatory bodies and accordingly, it has been attempted to find alternatives to these conventional flour and dough additives and the prior art has i.a. suggested the use of glucose oxidase for this purpose.
Thus, U.S. Pat. No. 2,783,150 discloses the addition of glucose oxidase to flour to improve dough strength and texture and appearance of baked bread.
CA 2,012,723 discloses bread improving compositions comprising cellulolytic enzymes such as xylanases and glucose oxidase, the latter enzyme being added to reduce certain disadvantageous effects of the cellulolytic enzymes (reduced dough strength and stickiness) and it is disclosed that addition of glucose to the dough is required to obtain a sufficient glucose oxidase activity.
JP-A-92-084848 suggests the use of a bread improving composition comprising glucose oxidase and lipase.
EP-B1-321 811 discloses the use of an enzyme composition comprising sulfhydryl oxidase and glucose oxidase to improve the rheological characteristics of doughs. It is mentioned in this prior art document that the use of glucose oxidase alone has not been successful.
In EP-B1-338 452 is disclosed an enzyme composition for improving dough stability, comprising a mixture of cellulase/hemicellulase, glucose oxidase and optionally sulfhydryl oxidase.
However, the use of glucose oxidase as a dough improving additive has the limitation that this enzyme requires the presence of sufficient amounts of glucose as substrate in order to be effective in a dough system and generally, the glucose content in cereal flours is low. Therefore, the absence of glucose in doughs or the low content hereof in doughs will be a limiting factor for the effectiveness of glucose oxidase as a dough improving agent.
In contrast hereto, the content of maltose in cereal flours is generally significantly higher than that of glucose and accordingly, a freshly prepared dough will normally contain more maltose than glucose. Thus, in an experiment where the content of sugars in supernatants from suspensions of wheat flour and a dough prepared from the flour and further comprising water, yeast, salt and sucrose (as described in the following example 2.3) were analyzed, the following values (% by weight calculated on flour) were found:
FlourDoughSucrose0.3<0.01Galactose0.0010.01Glucose0.250.72Maltose2.61.4Fructose0.080.67Lactose<0.01<0.01
In addition, the content of maltose remains at a relatively high level in a dough which is leavened by yeast, since the yeast primarily utilizes glucose, or it may even increase in the dough e.g. during proofing due to the activity of starch degrading enzymes such as e.g. β-amylase, which is inherently present in the flour or is added to the dough.
Whereas the prior art has recognized the useful improving effects of glucose oxidase on the rheological characteristics of bread doughs and on the quality of the corresponding baked products, it has also been realized that the use of this enzyme has several drawbacks. Thus, it may be required to add sucrose or glucose as substrate to the dough to obtain a sufficient effect and glucose oxidase does not constantly provide a desired dough or bread improving effect when used alone without the addition of other enzymes.
However, it has now been found that the addition of an oxidoreductase, which is capable of oxidizing maltose, including hexose oxidase as a sole dough conditioning agent, i.e. without concomitant addition of substrate for the added enzyme, or of other enzymes, to a farinaceous dough results in an increased resistance hereof to breaking when the dough is stretched, i.e. this enzyme confers in itself to the dough an increased strength whereby the dough becomes less prone to mechanical deformation. It is contemplated that this effect of addition of hexose oxidase to a dough is the result of the formation of cross-links between thiol groups in sulphur-containing amino acids in wheat gluten which occurs when the H2O2 generated by the enzyme in the dough reacts with the thiol groups which are hereby oxidized.
Hexose oxidase (D-hexose:O2-oxidoreductase, EC 1.1.3.5) is an enzyme which in the presence of oxygen is capable of oxidizing D-glucose and several other reducing sugars including maltose, glucose, lactose, galactose, xylose, arabinose and cellobiose to their corresponding lactones with subsequent hydrolysis to the respective aldobionic acids. Accordingly, hexose oxidases differ from glucose oxidase which can only convert D-glucose, in that hexose oxidases can utilize a broader range of sugar substrates. The oxidation catalyzed by the enzyme can be illustrated as follows:D-Glucose+O2→δ-D-gluconolactone+H2O2, orD-Galactose+O2→γ-D-galactogalactone+H2O2 
Hexose oxidase (in the following also referred to as HOX) has been isolated from several red algal species such as Iridophycus flaccidum (Bean and Hassid, 1956, J. Biol. Chem., 218:425-436) and Chondrus crispus (Ikawa 1982, Methods Enzymol., 89:145-149). Additionally, the algal species Euthora cristata (Sullivan et al. 1973, Biochemica et Biophysica Acta, 309:11-22) has been shown to produce HOX.
Other potential sources of hexose oxidase according to the invention include microbial species or land-growing plant species. Thus, as an example of such a plant source, Bean et al., Journal of Biological Chemistry (1961) 236: 1235-1240, have disclosed an oxidoreductase from citrus fruits which is capable of oxidizing a broad range of sugars including D-glucose, D-galactose, cellobiose, lactose, maltose, D-2-deoxyglucose, D-mannose, D-glucosamine and D-xylose. Another example of an enzyme having hexose oxidase activity is the enzyme system of Malleomyces mallei disclosed by Dowling et al., Journal of Bacteriology (1956) 72:555-560.
It has been reported that hexose oxidase isolated from the above natural sources may be of potential use in the manufacturing of certain food products. Thus, hexose oxidase isolated from Iridophycus flaccidum has been shown to be capable of converting lactose in milk with the production of the corresponding aldobionic acid and has been shown to be of potential interest as an acidifying agent in milk, e.g. to replace acidifying microbial cultures for that purpose (Rand, 1972, Journal of Food Science, 37:698-701). In that respect, hexose oxidase has been mentioned as a more interesting enzyme than glucose oxidase, since this latter enzyme can only be enzymatically effective in milk or other food products not containing glucose or having a low content of glucose, if glucose or the lactose-degrading enzyme lactase which convert the lactose to glucose and galactose, is also added.
The capability of oxidoreductases including that of hexose oxidase to generate hydrogen peroxide has also been utilized to improve the storage stability of certain food products including cheese, butter and fruit juice as it is disclosed in-JP-B-73/016612. It has also been suggested that oxidoreductases may be potentially useful as antioxidants in food products.
However, the present invention has demonstrated that hexose oxidase is highly useful as a dough conditioning agent in the manufacturing of flour dough products including not only bread products but also other products made from flour doughs such as noodles and alimentary paste products.